but got the impression we users of these "cheap Chinese Android boxes" were not welcome anymore.
Does not matter which OS you use, but it's a known fact that cheap Chinese boxes have questionable, highly variable hardware specs.
There are even fakes which you well know.
Then there is no open sourced code for U-Boot with these cheap Android chinese devices - which can lead to all sorts of issues. HDMI-CEC control being one of them.
With "Reference" hardware - think the VIM's, ODROID's, LePotato RPi etc - developers are dealing with known, common spec hardware where U-boot can also be properly modified. You also get direct contact with the hardware vendors - in English usually.
What all the developers are saying is it's a hell of a lot easier to code for something that is Reference hardware, which will be the same spec no matter what users buy.
Cheap Android devices have basically had a "free ride". And relied on the good will of guys like kszaq and others coding workarounds for them.
Expecting new Chipset spec hardware from cheap Chinese vendors to be fully Linux Kodi supported a few months after release is just fantasy stuff. It's why they only concentrate on specific devices.
No developer want to go out and buy this cheap chinese stuff either when Hardware vendors are getting software support for their devices, basically for free. The Hardware vendors get a great deal IMHO.